3D Heterostructured Copper Electrode for Conversion of Carbon Dioxide to Alcohols at Low Overpotentials

Abstract

to store intermittent renewable energy as well as closing the anthropogenic carbon cycle. [7,8] A wide array of metals, metal complexes, and hybrid catalysts based on Au, [9][10][11] Ag, [12][13][14] Sn, [15][16][17][18][19][20] Cu, [21][22][23] and Co [24][25][26] have been thoroughly investigated for CO 2 RR, however only Cu has been shown to generate ethanol and methanol with appreciable yield. Albeit, this unique property of Cu is also one of its major limitations as the metal produces numerous reduction products (such as CO, CH 4 , C 2 H 4 , formate, alcohols, and aldehydes) [27] that requires high applied overpotentials (≈1 V), [28,29] rendering the process to be expensive as the various liquid products would require separation as well as large input energy. These challenges can be circumvented by devising Cu + catalysts which can strongly bind the *CO radical (formed after electron and proton transfers to *CO 2˙− ) as a result of the adsorption of atomic O onto Cu + sites, allowing the possibility for further reduction to methanol and ethanol. [30][31][32][33][34] However, to date, Cu + catalysts have exhibited low Faradaic efficiency (FE) and current densities for ethanol and methanol production and suffers from stability issues, as the Cu + species can readily be reduced to Cu 0 during CO 2 RR. [21,35] Utilizing these insights as designing guidelines, it is crucial to develop inexpensive and stable Cu + species containing catalyst that can evade the aforementioned limitations of Cu catalysts.To address such challenges, a simple and inexpensive 3D heterostructured Cu sandwich electrode was prepared by subjecting commercially available copper foam (Cu-f) with a simple two-step fabrication process (anodization followed by annealing). The robust 3D interconnected porous structure of the Cu-f offers very high surface area and porosity that will assist in enhanced mass transport properties (including reactants and products), thereby making it an excellent contender for designing active electrodes. Through controlled anodization and annealing treatment, a greater quantity of Cu + /Cu 2+ interface was generated on the composite nanowires on Cu sandwich alongside more formation of oxygen vacancy defects. The as-synthesized catalyst exhibited improved selectivity toward methanol and ethanol production with a high current density. In addition to demonstrating enhanced activity for CO 2 RR, the Cu sandwich electrode also exhibited high activity for other catalytic reactions such as oxygen evolution reaction Active and cost-effective catalyst materials are required for electrochemical CO 2 reduction reactions (CO 2 RR) which, to date, are proving elusive. Here, the direct electrochemical conversion of CO 2 to liquid products with a high overall Faradaic efficiency (FE) by utilizing a unique 3D, heterostructured copper electrode (referred as Cu sandwich) that is obtained via a simple two-step treatment of commercially available copper foam is reported. The designed catalyst achieves an FE toward liquid products of >50...

Modulating Activity through Defect Engineering of Tin Oxides for Electrochemical CO2 Reduction

“…[39] It can be observed from Figure 4a, the intensity ratio between defects and the resonant A 1g phonon (I defect /I A1g ) was maximized for FSP-SnO 2 -5 (I defect /I A1g = 1.36) followed by FSP-SnO 2 -7 (I defect /I A1g = 1.25) and the lowest was for FSP-SnO 2 -3 (I defect /I A1g = 1.02). [44] It has been reported that OHC sites, alongside the radicals, assists in the binding of CO 2 reactants, [25,38,45] as well as active sites to stabilize the formate anion radical intermediate. UV-vis carried out with FSP-SnO 2 -5 further indicated that these defects are not changing the electronic states of the catalyst ( Figure S11, Supporting Information).…”

A Disquisition on the Active Sites of Heterogeneous Catalysts for Electrochemical Reduction of CO2 to Value‐Added Chemicals and Fuel

“…Zeng and co‐workers proposed an efficient strategy to facilitate CO 2 activation with surface‐rich oxygen vacancies in ZnO nanosheets by H 2 plasma treatment . The introduction of oxygen vacancies increases the charge density of ZnO resulting in the enhanced CO generation with j and maximum FE of −16.1 mA cm −2 and 83%, respectively at −1.1 V. Recently, oxygen vacancies on Cu‐based catalysts can be tuned toward electrocatalytic CO 2 reduction to generate ethylene and ethanol . Gu et al reported that partially reduced Cu oxide nanodendrites with surface‐rich oxygen vacancies serving as excellent Lewis base sites for enhanced adsorption of *CO 2 and the release of *CH 2 which were further hydrogenated to form ethylene .…”

“…The maximum FE C2H4 and its corresponding partial j are 63% and −18.5 mA cm −2 , respectively at operating potential of −1.4 V. Similarly, we also proposed a strategy to produce a unique three‐dimensional heterostructured Cu electrode via two‐step treatments including anodization and calcination. The as‐synthesized copper electrode can convert CO 2 to ethanol with FE of 31% and a stable current density of −1.3 mA cm −2 at low overpotential of −0.3 V . The enhanced activity of the electrocatalyst was attributed to the formation of abundant Cu + /Cu 2+ , which can be stabilized by the presence of oxygen vacancy defects.…”

“…Data from refs. . The detailed catalytic activity of these catalysts is presented in Table S3 (Supporting Information).…”

“…[191] The introduction of oxygen vacancies increases the charge density of ZnO resulting in the enhanced CO generation with j and maximum FE of −16.1 mA cm −2 and 83%, respectively at −1.1 V. Recently, oxygen vacancies on Cu-based catalysts can be tuned toward electrocatalytic CO 2 reduction to generate ethylene and ethanol. [192,193] Gu et al reported that partially reduced Cu oxide nanodendrites with surface-rich oxygen vacancies serving as excellent Lewis base sites for enhanced adsorption of *CO 2 and the release of *CH 2 which were further hydrogenated to form ethylene. [192] The maximum FE C2H4 and its corresponding partial j are 63% and −18.5 mA cm −2 , respectively at operating potential of −1.4 V. Similarly, we also proposed a strategy to produce a unique Adv.…”